Learn SQL Step by Step

SQL COUNT

SQL Server COUNT() function is an aggreagate function that returns the number of rows in a table . It sets the number of rows or non NULL column values.

SQL Server DELETE

SQL delete statement is used to delete records from table based on specific conditions which are passed in where clause.

SQL SERVER UPDATE

SQL UPDATE Statement is used to modify an existing
records in table .

SQL TRUNCATE TABLE

SQL TRUNCATE TABLE statement is used to delete complete data from an existing table. It is similar to a delete statement without a WHERE clause.

Primary Key VS Composite Key?

A PRIMARY KEY constraint uniquely identifies each record in a table .

A COMPOSITE KEY is a combination of two or more columns in a table that can be used to uniquely identify each row in the table when the columns are combined uniqueness is guaranteed, but when it taken individually it does not guarantee uniqueness.

SQL DROP TABLE

SQL DROP TABLE statement is used to delete the table from database.

SQL ALTER TABLE

SQL ALTER TABLE statement is used to modify the data type of a column , add a new column ,delete an old column from table and add a new constraints and remove an existing constraints on table.